NKT cells are innate-like T cells and tend to reside in non-lymphoid tissues and to have markers of chronically activated or memory cells. When activated, NKT cells exhibit a fast and more robust effector function such as cytokine release or cytotoxicity. They are thought to serve as a bridge between the rapidly occurring innate immunity and the more slowly occurring adaptive immunity. Thymus-derived NKT cells undergo further differentiation and functional specialization in the periphery that promotes their migratio into non-lymphoid tissues such as the liver and adipose tissue. Therefore, NKT cells are a heterogeneous population with a high degree of phenotypic and functional specialization in non-lymphoid tissues. The recent studies in different clinical and experimental settings showed that while NKT cells are more often pathogenic, they are also regulatory. NKT cells are abundant in the liver and adipose tissue, two organs that play a critical role in the development of metainflammation. Recently, the signaling pathways that control cellular metabolism have been shown to have a crucial role in dictating the outcome of T cell activation and effector function. Distinct T cell subsets adopt metabolic programs specific to support their needs. Upon T cell activation, reactive oxygen species (ROS) is produced by mitochondria, which is required for T-cell activation. Substantial evidence has revealed that ROS are essential second messengers in innate and adaptive immune cells. Yet increased levels of ROS within immune cells can result in hyperactivation of inflammatory responses, resulting in tissue damage and pathology. Although much effort has put forth to understand metabolic needs and regulation of CD4 and CD8 T cells, little is known about the metabolic regulation of NKT cells. Our preliminary studies showed that freshly isolated NKT cells from the liver have high ROS than CD4 T cells, whereas NKT cells resident in visceral adipose tissue show low ROS similar to CD4 T cells. Interestingly, NKT cells in these two tissues have an opposing function. Based on the published studies and our preliminary data, we hypothesize that the breakdown of tolerance of cell metabolism of NKT cells leads to inflammation and tissue damage resulting in autoimmune hepatitis and obesity. To test the hypothesis, we will investigate the metabolic regulation in NKT cells and how cell metabolism of NKT cells regulates two distinct metabolic immune diseases, liver inflammation and obesity. Given the importance of NKT cells as a critical factor for immune diseases, studying the regulation of cell metabolism, oxidative stress and immune diseases mediated by NKT cells is highly innovative and significant.